I. Technical Field
The present invention relates to a dynamic bearing device. This bearing device is suitable for: a spindle motor for information equipment, for example, a magnetic disk device such as an HDD or an FDD, an optical disk device for a CD-ROM, a DVD-ROM or the like, and a magneto-optical disk device for an MD, an MO or the like; a polygon scanner motor for a laser beam printer (LBP); and a small motor for electric equipment, for example, an axial fan and the like.
II. Description of Related Art
The above-mentioned various motors are required to operate not only with high rotational accuracy but also at higher speed, lower cost, and lower noise. One of the components determining the required performance is a bearing for supporting a spindle of the motor. As this type of bearing, a dynamic bearing device having characteristics excellent in the above-mentioned required performance has been considered for use or has been put into practical use in recent years.
As an example of the dynamic bearing device, Japanese Patent Laid-Open Publication No. 2002-61641 discloses a dynamic bearing device having the following structure. The dynamic bearing device includes: a cylindrical housing with a closed end; a bearing member fixed to an inner periphery of the housing; a shaft member inserted onto an inner peripheral face of the bearing member; and a radial bearing portion and a thrust bearing portion, which rotatably support the shaft member in a non-contact manner by a dynamic pressure effect generated during the relative rotation of the shaft member and a bearing sleeve.
Of the radial bearing portion and the thrust bearing portion, the thrust bearing portion generates a pressure by a dynamic pressure effect of oil in each of thrust bearing gaps between both end faces of a flange of the shaft member and a bottom face of the housing and an end face of the bearing sleeve, which are opposed thereto, so as to support the shaft member in an axial direction in a non-contact manner.
In this type of dynamic bearing device, a member on the rotational side and a member on the fixed side inevitably slide with each other at high speed when the dynamic bearing device starts and stops operating. Therefore, in the dynamic bearing device used for information equipment in which the operation of a motor is frequently started and stopped, for example, consumer equipment including an HDD-DVD recorder and a storage device for a cell-phone, the wear of a sliding face caused by repeated start and stop of the operation emerges as a problem under some conditions for use and the like. Thus, wear resistance is desired to be further improved. In particular, in the case where the flange is made of a resin, wear is more likely to be accelerated as compared with the case where metals slide with each other. Accordingly, there is a possibility that bearing performance may be degraded within a short period of time due to the effect of abrasion powder.